1. Field of the Invention
The present invention relates to optical equipment and, more specifically but not exclusively, to optical fiber amplifiers.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
An optical amplifier is a device that amplifies an optical signal directly in the optical domain without converting the optical signal into a corresponding electrical signal. Optical amplifiers are widely used, for example, in the fields of optical communications and laser physics.
One type of an optical amplifier is a doped-fiber amplifier, with a well-known example being the Erbium-doped fiber amplifier (EDFA). In operation, a signal to be amplified and a pump beam are multiplexed into the doped fiber. The pump beam excites the doping ions, and amplification of the signal is achieved by stimulated emission of photons from the excited dopant ions.
Another type of an optical amplifier is a Raman amplifier, which relies on stimulated Raman scattering (SRS) for signal amplification. More specifically, when a signal to be amplified and a pump beam are multiplexed into an optical fiber made of an appropriate material, a lower-frequency signal photon induces SRS of a higher-frequency pump photon, which causes the pump photon to pass some of its energy to the vibrational states of the fiber material, thereby converting the pump photon into an additional signal photon. The pump beam may be coupled into the fiber in the same direction as the signal (co-directional pumping) or in the opposite direction (contra-directional pumping).